The dosing of gold salts for progressive rheumatoid arthritis is largely empirical. The present study is aimed at elucidating the pharmacokinetics of gold sodium thiomalate in arthritics in an attempt to develop individualized dosing regimens that minimize toxicity and maximize therapeutic benefit. One aspect of the study is designed to monitor gold concentrations in plasma, whole blood and saliva in patients on chronic gold therapy and correlate these concentrations to laboratory and physical findings related to therapeutic benefit and toxicity. Preliminary results in eight patients indicate 3.0-4.0 mcg/ml as a minimum plasma gold trough concentration necessary for therapeutic benefit. The development of gold rash accompanied by high RBC:plasma gold radios. This represents the present trend in the data and is not meant to be conclusive, given the number of patients in the study. Necessary to the successful completion of this project was the development of an analytical method to measure gold concentration in body fluids. We have developed a rapid method, using atomic absorption, which is highly reproducible and sensitive. Gold is extracted from the body fluid into methyl isobutyl ketone and the organic layer is injected into the carbon furnace of a spectrophotometer. The sensitivity of the assay is 0.05 mcg/ml and calibration curves are linear up to 0.75 mcg/ml (r is greater than or equal to 0.996).